Game theory and animal contest behaviour

by Gareth Arnott & Irene Camerlink


Game theory is a branch of applied mathematics, initially developed by economists to model human strategic decision making, and popularised with well-known examples such as the Prisoner’s dilemma, and Russell Crowe’s portrayal of the Nobel laureate John Nash in the film A Beautiful Mind. However, biologists were quick to spot the utility of game theory for evolutionary biology. Amongst them was John Maynard Smith who was the first to apply game theory to the study of animal contests, producing the now classic ‘Hawk/Dove’ game (1). This demonstrated the idea of an evolutionarily stable strategy (ESS) such that frequency dependent selection will result in a population of ‘aggressive’ hawks and ‘non-aggressive’ doves with the proportions of each depending on the costs and benefits of fighting.

The hawk/dove model set the scene for the development of more realistic game theory models of animal contests that incorporated opponent asymmetries in fighting ability, termed resource holding potential (RHP), a concept that aims to capture the potential of the individual to win a fight, and is based on differences such as body weight or weapon size. In addition, the models incorporated various information gathering strategies regarding own and opponent fighting ability and the value of the contested resources (for review see 2).

The utility of this approach is that the models yield testable predictions regarding contest outcomes and fighting durations for winners and losers which have been seized upon by empiricists. One aspect of current debate is the extent of information gathering that actually occurs during a contest. For example, some models assume opponents assess relative fighting ability, also entering popular culture with terms used in wildlife documentaries of competing animals like ‘they are sizing each other up’. This is termed mutual assessment and we humans excel at this. However, some models are based on an alternative assumption, termed self assessment, in which animals only have information about their own fighting ability, being unable to assess the opponent. Indeed, contrary to our human abilities and assumptions, in recent years there has been accumulating evidence for self assessment in animal contests, leading to calls for researchers to carefully test for mutual assessment, rather than assume that it occurs.

Photo by Marianne Farish illustrating pigs 'sizing each other up'
Photo by Marianne Farish illustrating pigs ‘sizing each other up’


While game theory has been influential for furthering our understanding of animal contest behaviour in an evolutionary biology setting, more recently it has also been applied to human warfare (e.g. 3). Moreover, the authors are currently translating game theoretical principles to study aggression as an applied animal welfare issue of captive animals (4, 5), examining aggression in pigs upon regrouping (a routine procedure in commercial farming which results in intense aggression).


  1. Maynard Smith, J. & Price, G. R. (1973). The Logic of Animal Conflict. Nature, 246, 15-18.
  2. Arnott, G., & Elwood, R. W. (2009). Assessment of fighting ability in animal contests. Animal Behaviour, 77(5), 991-1004.
  3. Briffa, M. (2014). What determines the duration of war? Insights from assessment strategies in animal contests. PloS one, 9(9), e108491.
  4. Camerlink, I., Turner, S. P., Farish, M., & Arnott, G. (2015). Aggressiveness as a component of fighting ability in pigs using a game-theoretical framework. Animal Behaviour, 108, 183-191.
  5. Camerlink, I., Arnott, G., Farish, M., & Turner, S. P. (2016). Complex contests and the influence of aggressiveness in pigs. Animal Behaviour, in press.


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